An abnormal chromosome number, aneuploidy, is a common characteristic of tumor cells. Boveri proposed nearly 100 years ago that aneuploidy causes tumorigenesis, but this has remained untested due to the difficulty of selectively generating aneuploidy. Cells and mice with reduced levels of the mitosis-specific, centromere-linked motor protein CENP-E are now shown to develop aneuploidy and chromosomal instability in vitro and in vivo. An increased rate of aneuploidy does drive an elevated level of spontaneous lymphomas and lung tumors in aged animals. Remarkably, however, in examples of chemically or genetically induced tumor formation, an increased rate of aneuploidy is a more effective inhibitor than initiator of tumorigenesis. These findings reveal a role of aneuploidy and chromosomal instability in preventing tumorigenesis.

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The antitumor drug Taxol stabilizes microtubules and reduces their dynamicity, promoting mitotic arrest and cell death. Upon assembly of the ␣͞␤-tubulin heterodimer, GTP bound to ␤-tubulin is hydrolyzed to GDP reaching a steady-state equilibrium between free tubulin dimers and microtubules. The binding of Taxol to ␤-tubulin in the polymer results in cold-stable microtubules at the expense of tubulin dimers, even in the absence of exogenous GTP. However, there is little biochemical insight into the mechanism(s) by which Taxol stabilizes microtubules. Here, we analyze the structural changes occurring in both ␤-and ␣-tubulin upon microtubule stabilization by Taxol. Hydrogen͞deuterium exchange (HDX) coupled to liquid chromatography-electrospray ionization MS demonstrated a marked reduction in deuterium incorporation in both ␤-and ␣-tubulin when Taxol was present. Decreased local HDX in peptic peptides was mapped on the tubulin structure and revealed both expected and new dimer-dimer interactions. The increased rigidity in Taxol microtubules was distinct from and complementary to that due to GTP-induced polymerization. The Taxol-induced changes in tubulin conformation act against microtubule depolymerization in a precise directional way. These results demonstrate that HDX coupled to liquid chromatography-electrospray ionization MS can be effectively used to study conformational effects induced by small ligands on microtubules. The present study also opens avenues for locating drug and protein binding sites and for deciphering the mechanisms by which their interactions alter the conformation of microtubules and tubulin dimers.hydrogen͞deuterium exchange

A structure-activity relationship (SAR) study of the South African willow tree (Combretum caffrum) antineoplastic constituent combretastatin A-4 (1b) directed at maintaining the (Z)-stilbene relationship of the olefin diphenyl substituents led to synthesis of a potent cancer cell growth inhibitor designated phenstatin (3b). Initially phenstatin silyl ether (3a) was unexpectedly obtained by Jacobsen oxidation of combretastatin A-4 silyl ether (1c --> 3a), and the parent phenstatin (3b) was later synthesized (6a --> 3a --> 3b) in quantity. Phenstatin was converted to the sodium phosphate prodrug (3d) by a dibenzyl phosphite phosphorylation and subsequent hydrogenolysis sequence (3b --> 3c --> 3d). Phenstatin (3b) inhibited growth of the pathogenic bacterium Neisseriagonorrhoeae and was a potent inhibitor of tubulin polymerization and the binding of colchicine to tubulin comparable to combretastatin A-4 (1b). Interestingly, the prodrugs were found to have reduced activity in these biochemical assays. While no significant tubulin activity was observed with the phosphorylated derivative of combretastatin A-4 (1d), phosphate 3d retained detectable inhibitory effects in both assays.